Circulating memories are known in which the bits of a calling code, specifically a 4-bit digital code, are stored together with associated address bits in a time slot temporarily assigned to them. In such a system, a time slot vacated by the extraction of a stored code word is subsequently filled with a new code word from an input register; since the read-out of the code words from the memory occurs on the basis of the availability of outgoing channels leading to their respective destinations, rather than in a sequential manner according to their order of appearance in a memory cycle, the original sequence of entry of the code words cannot be preserved and each code word must be tagged with a supplemental set of bits indicating its relative time position. These supplemental bits require, of course, a corresponding storage capacity of the circulating memory in each time slot.